A specifying location system which detects the locations of radio communication terminal units, e.g., cellular phone units, performs based on the IS (Interim Standard) 801 protocol. The sequential operations implemented under IS 801 protocol is shown in FIG. 8.
As shown in FIG. 8, a cellular phone unit 1 is instructed by the user to find its location. It makes access to nearby base stations thereby to get base station information of these base stations (step 101), transmits the base station information to a location information server 15, and requests the server to release assistant information useful for the access to GPS (Global Positioning System) satellites.
The location information server 15, upon receiving the base station information from the cellular phone unit 1, specifies or determines the approximate location of the phone unit based on the received base station information, and it responds to the request of assistant information to compute assistant information useful for the cellular phone unit to make access to GPS satellites and send the computed assistant information to the phone unit 1 (step 151).
The cellular phone unit 1, upon receiving the assistant information from the location information server (15), makes access to GPS satellites based on the assistant information thereby to get GPS satellite information of the GPS satellites, makes access to the base stations again to get their base station information again, sends the obtained GPS satellite information and base station information to the location information server, and requests the server to release the specified location.
The location information server 15 receives the GPS satellite information, base station information and request of specifying location from the cellular phone unit 1, detects the location of phone unit based on the received information, and sends the specified location to the phone unit 1 (step 152).
This system enables the cellular phone unit 1 to make access to GPS satellites based on the assistant information provided by the location information server 15, instead of having to keep almanac information by itself. It is advantageous for the whole system to minimize the time before the start of location specifying operation and also advantageous for each cellular phone unit to reduce its overhead operation based on the reliance of location specifying operation on the location information server.
In regard to the above sequential operations, the cellular phone unit 1 sends to the location information server 15 all of GPS satellite information resulting from the access to GPS satellites and base station information resulting from the access to base stations. Therefore, it is likely that information which is unnecessary or even detrimental for the location specifying operation to the location information server 15 is sent. In this case, the location information server 15 might not be able to detect the location of phone unit accurately. Another drawback is a considerable communication toll and time imposed on the transmission of GPS satellite information and base station information.